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Chitosan-xanthan gum PEC-based aerogels: A chemically stable PEC in scCO2
Tomé, Luciana I. N.; Reis, Marco S.; Sousa, Hermínio C. de; Braga, Mara E. M.An innovative aerogel obtained from a chitosan/xanthan gum polyelectrolyte complex (PEC) was developed in this work from the screening of thirteen different combinations of natural polyelectrolytes: two positively charged biopolymers (chitosan and gelatin A), six negatively-charged biopolymers (pectin, iota-carrageenan, collagen, xanthan gum, alginate and modified galactomannan), and a neutral polymer (guar gum...
Measurements and Correlation of High-Pressure Densities of Imidazolium-Based Io...
Tomé, Luciana I. N.; Carvalho, Pedro J.; Freire, Mara G.; Marrucho, Isabel M.; Fonseca, Isabel M. A.; Ferreira, Abel G. M.; Coutinho, João A. P.In the present work, experimental density measurements are reported along with the derived thermodynamic properties, such as the isothermal compressibility (κT), the isobaric expansivity (αp), and the thermal pressure coefficient (γv) for imidazolium-based ionic liquids (ILs), namely, 1-ethyl-3-methylimidazolium methylsulfate [C2mim][MeSO4], 1-ethyl-3-methylimidazolium ethylsulfate [C2mim][EtSO4], 1,3-diethylim...
Enthalpy of sublimation/vaporization of trans-cyclohexyl-1,4-diamine and cis-cy...
Tomé, Luciana I. N.; Rosado, Mário T. S.; Nunes, Sandra C. C.; Maria, Teresa M. R.; Canotilho, João; Eusébio, M. Ermelinda S.The molar enthalpy of sublimation, , of trans-cyclohexyl-1,4-diamine and the molar enthalpy of vaporization, , of cis-cyclohexyl-1,2-diamine, at the temperature 298.15 K, were determined by calorimetry. was obtained for the trans-isomer and for the cis form. The molar enthalpy of fusion of the first compound, at T = 342.1 K, was determined by differential scanning calorimetry. The molar enthalpy of vaporization...
Solvation enthalpy and the thermodynamics of hydration of trans-cyclohexyl-1,4-...
Tomé, Luciana I. N.; Jesus, A. J. Lopes; Castro, R. A. Esteves de; Teixeira, M. Helena S. F.; Canotilho, João; Eusébio, M. Ermelinda S.The enthalpy of solution of trans-cyclohexyl-1,4-diamine and cis-cyclohexyl-1,2-diamine in water was determined by calorimetry. The enthalpy of hydration was determined from this quantity and from the enthalpy of sublimation/vaporization presented in another paper by the authors. Considering the solvation process resulting from cavity creation in the solvent and variation of solute conformation transfer steps, ...
Molecular structure of mono- and 1,2-aminoderivatives of cyclohexane: Steric st...
Tomé, Luciana I. N.; Rosado, Mário T. S.; Eusébio, M. Ermelinda S.; Redinha, J. S.The conformational study of cyclohexylamine and 1,2-cyclohexylamine derivatives was performed. The potential energy surface of every compound was calculated at B3LYP/6-31G(d) and the conformational energy minima were further optimized at B3LYP/aug-cc-pVDZ level of theory. The geometrical parameters and the electronic energy of each conformer were determined. The internal energy, enthalpy, entropy, Gibbs energy ...
Enthalpy of Sublimation in the Study of the Solid State of Organic Compounds. A...
Jesus, A. J. Lopes; Tomé, Luciana I. N.; Eusébio, M. Ermelinda; Redinha, J. S.The enthalpies of sublimation of erythritol and l-threitol have been determined at 298.15 K by calorimetry. The values obtained for the two diastereomers differ from one another by 17 kJ mol-1. An interpretation of these results is based on the decomposition of this thermodynamic property in a term coming from the intermolecular interactions of the molecules in the crystal (ΔintH°) and another one related with ...
Conformational study of erythritol and threitol in the gas state by density fun...
Jesus, António J. Lopes; Tomé, Luciana I. N.; Rosado, Mário Túlio S.; Leitão, M. Luísa P.; Redinha, José S.Density functional theory calculations using the B3LYP functional and the 6-311++G(d,p) basis set were carried out on the isolated molecules of erythritol and L-threitol. For the meso isomer, a relatively large number of conformers have to be considered to describe the gas state structure. The lowest energy conformer is characterized by the establishment of a strong intramolecular H-bond between the two termina...